chore: check if discount_percentage exists
chore: check if discount_percentage exists

fixes TypeError: '>' not supported between instances of 'NoneType' and 'float'

Signed-off-by: Chinmay D. Pai <ab3234b32bd9ecd2892f3eb0b557ab584a8ff0cf@gmail.com>

gsnbng/erpnext,gsnbng/erpnext,gsnbng/erpnext,gsnbng/erpnext